Thingm produce a small USB LED dongle that blinks (Blink(1)!). It was a Kickstarter project that sold really well and is brilliant to use as a notification device. There are many apps to use it, from a small command line tool to GUI ones (e.g. a twitter notifier etc...).

Okay, I think I see the issue. I guess Gentoo doesn't use "pkg-config", which is what the Makefile is currently using to determine how libusb was installed.

In that case, try building with:
LIBS+=-L/usr/lib make

That will force "/usr/lib" into the library search path during linking.

If anyone reading this is a Gentoo hacker, what's the preferred way of determining package compilation options, a la "pkg-config"?

That does not work. However, are they on the right tracks?_________________Climb up it, kayak down it + make sure it runs on GNU/Linux
"cease to exist, giving my goodbye, drive my car into the ocean,
you think I'm dead, but i sail away, on a wave of mutilation!"

Hi ferg, if you haven't figured it out already part of the problem is that the Makefile ThingM provides builds a statically linked binary. I think very few things in Portage require a static version of libusb, so it's unlikely you have the necessary files.

Try either emerging libusb with the static-libs USE flag enabled or give this patch a try:

Now for blinking goodness! I'm using it to alert me when a person walks past a motion detecting camera._________________Climb up it, kayak down it + make sure it runs on GNU/Linux
"cease to exist, giving my goodbye, drive my car into the ocean,
you think I'm dead, but i sail away, on a wave of mutilation!"